Pandora, Slacker, or iTunes Radio?

Which service do you prefer? Or do you just use the radio options in spotify or Rdio? Something different?

Right now, I'm liking Rdio for my on demand song needs, but I'm looking for something for streaming radio use. And I can't decide between pandora, slacker , or ITunes Radio. Anyone used these and can offer feedback?

Despite having tried several different times over the past few years to like Slacker I just can't. Library seems large enough but, I just can't seem to get the content to ever appeal to me for some reason.

I've currently settled on Songza for the past several months as it seems to suit my listening needs the best. I'm located in Canada so I don't have access to Pandora, Beats, iTunes Radio and several others (at least without workarounds I couldn't be bothered with) but, I have found that Songza does offer a quality experience for both iPhone and iPad.